Method _updateSelectedItemIndex

src/cdk/stepper/stepper.ts:545–569

(newIndex: number)

  }

  private _updateSelectedItemIndex(newIndex: number): void {
    const stepsArray = this.steps.toArray();
    const selectedIndex = this._selectedIndex();

    this.selectionChange.emit({
      selectedIndex: newIndex,
      previouslySelectedIndex: selectedIndex,
      selectedStep: stepsArray[newIndex],
      previouslySelectedStep: stepsArray[selectedIndex],
    });

    // If focus is inside the stepper, move it to the next header, otherwise it may become
    // lost when the active step content is hidden. We can't be more granular with the check
    // (e.g. checking whether focus is inside the active step), because we don't have a
    // reference to the elements that are rendering out the content.
    if (this._keyManager) {
      this._containsFocus()
        ? this._keyManager.setActiveItem(newIndex)
        : this._keyManager.updateActiveItem(newIndex);
    }

    this._selectedIndex.set(newIndex);
    this.selectedIndexChange.emit(newIndex);
    this._stateChanged();
  }

  _onKeydown(event: KeyboardEvent) {
    const hasModifier = hasModifierKey(event);